SELECTION OF CHINESE-HAMSTER OVARY CELLS (CHO-K1) WITH REDUCED GLUTAMATE AND ASPARTATE UPTAKE

Transport of L-[H-3]glutamate into Chinese hamster ovary cells (CHO-K1 ) was characterized and the results used to design a tritium suicide s election for cells with transport defects. Replicas of surviving colon ies on polyester cloth disks were screened by autofluorography for red uced uptake and two mutant clones, Ed-A1 and Ed-B8, were obtained. Upt ake of glutamate through a sodium-dependent system in both mutants was characterized by significant reductions in V(max) and increases in K( m) compared to parental cells, but their response to removal of extrac ellular sodium differed, suggesting distinct mutations in the two line s. The V(max) of aspartate uptake through this system was reduced in b oth mutants, to one-ninth in the case of Ed-B8. Glutamate uptake throu gh a sodium-independent system was not altered in either mutant. Surpr isingly, acid-soluble intracellular pools of several amino acids were higher in both mutants.